The present invention relates in general cathode ray tubes used in display systems, and in particular, to color displays using cathode ray tubes that installed in data processing systems that are marketed world wide.
Cathode ray tube (CRT) displays are used in televisions, most computer displays and many other displays and monitors. Color CRTs create images by impinging an electron beam on the face of an evacuated glass tube that has been coated with phosphors that emit light at the primary colors. The intensity of the colors depends on the intensity of the electron beam that impinges on the particular emission phosphor.
To create a full screen image the electron beams are scanned in a raster and modulated electronically. Moving electrons are affected by and undergo a force if they are moving in a magnetic field. Since CRTs are manufactured in very large volumes, the CRTs are adjusted or xe2x80x9cyammedxe2x80x9d at the site of manufacture. These adjustments are made to insure that images are placed on the screen or face of the tube for correct viewing. Since the earth has a magnetic field, adjustments made at one point of manufacture may cause viewing errors when the CRT is shipped to a another geographic location, e.g. another hemisphere. Some manufacturers of color CRTs have incorporated correction circuitry to electronically correct for variations in the earth""s magnetic field.
Providing CRTs that were adjusted in the factory to compensate for the earth""s magnetic field at the point of use was one of the lowest cost ways to correct the problem. In the early development of color CRTs as many as seven different part numbers were used at times to account for the variations in the earth""s magnetic field at various geographic locations. However, advances in CRT manufacture has reduced to three the number of different CRTs of a type that are manufactured and adjusted for variations in the earth""s magnetic field; one for the northern, southern, and equatorial hemispheres.
Since multiple part numbers in any high volume part may create cost and inventory problems, it would be advantageous to further reduce the number of part numbers for CRTs since they are shipped to every part of the world. A method for reducing the number of CRT part numbers that is simple and cost effective is needed. Further, it would be beneficial if the CRT manufacturing method that reduced the number of part numbers also allowed CRTs manufactured in one area to be easily adapted to another.
The present invention discloses a method for reducing the part numbers on CRTs manufactured for shipment worldwide. The method includes the steps to produce only two part numbers instead of three normally used for northern hemisphere, southern hemisphere and equatorial hemisphere distribution. The CRT is made and adjusted so that the southern and northern hemisphere parts are symmetrical relative to their magnetic field bias to account for the earth""s magnetic field. To account for the different CRT magnetic field bias needed for the southern and northern hemispheres, the CRT is installed in either normal or inverted orientation. The yoke design for the CRT of the present invention has a connector that can also be installed in either the normal or the inverted connector orientation. The yoke connector enables signals and signal routing so the start scan is in the upper left corner of the CRT when it is in either the normal or inverted orientation. The present invention also has the wiring points to the neck video card that enable proper routing in either the normal or inverted installation of the CRT. The symmetrical design of the CRT and the disclosed configuration of the yoke connections and the neck video card connections a design that reduces to two the CRTs needed for color CRT displays shipped to the, southern, northern, or equatorial hemispheres. The present invention also enables simple conversion of the southern or northern hemisphere CRT by rotating the CRT 180 degrees when installed in a system configured for shipment to either the southern and northern hemisphere.
The various parts of the CRT system that are altered for the different installations, CRT, yoke connector and neck video card connectors may also have visual indicators to show when all of the elements are in a correct orientation for a given installation.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.